216 PRACTICAL ORGANIC CHEMISTRY
(4 hours). The viscous mass is melted in boiling water, trans-
ferred to a round flask (ij litre) and distilled in steam until no
more dimethylaniline passes over. On cooling, the base adheres
to the flask and is washed by decantation. It is recrystallised
from absolute alcohol and is colourless. The yield is nearly
theoretical. This is the leuco-base, and is formed according to
the following equation :
CGH5CHO + 2C0H6N(CH,)2 - CGH5CH/ +H2O.
It is converted into the colouring matter by oxidation. Ten
grams of the base are dissolved by slightly warming with dilute
hydrochloric acid containing exactly 27 grains of hydrogen
chloride (made by diluting cone, hydrochloric acid with twice its
volume of water and then determining the specific gravity or
titrating with standard caustic soda). The liquid is diluted with
800 c.c. water, and 10 grains of a 40 per cent, acetic acid solution
added. The mixture is cooled with a few lumps of ice, and a
thin paste of freshly precipitated lead peroxide containing exactly
7*5 grams PbO2 (estimated by drying a small weighed sample on
the water-bath) is added in the course of five minutes with
frequent shaking. The product is left 5 minutes, and then a
solution of 10 grams sodium sulphate in 50 c.c. water is run in
and the solution filtered from lead sulphate. To the filtrate a solu-
tion of 8 grams zinc chloride in a little water is added, and then a
saturated solution of common salt until no more of. the dye is
thrown down. It is filtered, and recrystallised by dissolving in
water and adding salt solution. Yield, 80 per cent, of the theory
of zinc salt.
\CBH4N(CH3)2 . \C6H4:N(CH3)2C1
See Appendix., p. 313.
C6H5CH< + 0 + HQ=C/C6H4N(CH,)o +H2O.
i Naphthalene, C10H8
, Naphthalene is obtained from the "middle oil" in the distil-
j lation of coal-tar. It crystallises in colourless, glistening plates,
Jj which have a characteristic smell.
\\ ' Properties.— -M. p. 80°; b. p. 218°; sp. gr. 1-145 at 4°. It